Polyphenylsilsesquioxanes are used in such applications as coating materials, sealing materials, and interlayer insulation membranes on account of their excellent heat resistance and electrical insulation.
Examples of such polyphenylsilsesquioxanes are cage octaphenylsilsesquioxane prepared by hydrolyzing phenyltrichlorosilane in an organic solvent into phenyltrihydroxysilane and polycondensing the hydrolysis product under heat in an anhydrous solvent in the presence of an alkaline rearrangement and condensation catalyst, phenylsiloxane prepolymers of low intrinsic viscosity prepared by separating the aforementioned cage octaphenylsilsesquioxane and polymerizing it under heat again in the presence of an alkaline rearrangement and condensation catalyst, and phenylsilsesquioxanes of high intrinsic viscosity prepared by further polymerizing the aforementioned prepolymers under heat in the presence of an alkaline rearrangement and condensation catalyst [Japan Tokkyo Koho Sho 40-15,989 (1965), Japan Kokai Tokkyo Koho Sho 50-139,990 (1975), and J. Polymer Sci., Part C, No. 1, pp 83-97 (1963)].
Ladder polyorganosiloxanes with their side chains partly modified by introduction of reactive functional groups are disclosed, for example, in Japan Kokai Tokkyo Koho Hei 3-281,616 (1991), Japan Kokai Tokkyo Koho Hei 4-33,936 (1992), and Japan Kokai Tokkyo Koho Sho 62-215,944 (1987). Moreover, polyorganosilsesquioxanes in which the hydrogen atoms of the silanol groups are wholly or partly replaced with a triorganosilyl group are described in Japan Kokai Tokkyo Koho Sho 61-221,232 (1986), Japan Kokai Tokkyo Koho Hei 2-32,356 (1990), Japan Kokai Tokkyo Koho Hei 4-185,641 (1992), Japan Kokai Tokkyo Koho Hei 4-353,521 (1992), and EURO. PAT. No. 0516144A1. Many of these disclosures aim mainly at improving the storage stability of ladder polyorganosilsesquioxanes by deactivation of the terminal silanol groups (there is still a room for argument about whether it is terminal group or internal defect) or terminating the polycondensation of polyorganosilsesquioxanes by addition of a silylating agent for control of the molecular weight, that is, effecting end-capping.
The following procedures are known for end-capping: polyorganosilsesquioxanes containing unreacted silanol groups are first synthesized and then allowed to react with a triorganochlorosilane in the presence of an alkali catalyst such as pyridine to effect dehydrochlorination or, in a similar manner, polyorganosilsesquioxanes containing silanol groups are allowed to react with an organomonoisocyanatosilane [Japan Kokai Tokkyo Koho Sho 61-221,232 (1986) and Japan Kokai Tokkyo Koho Sho 63-13,446 (1988); polyorganosilsesquioxanes containing terminal hydroxyl groups are synthesized purposefully and allowed to react either with a triorganomonoalkoxysilane to effect dealkanolation [Japan Kokai Tokkyo Koho Sho 57-12,057 (1982) and Japan Kokai Tokkyo Koho Sho 60-110,726 (1985)] or with a triorganomonochlorosilane to effect dehydrochlorination [Japan Kokai Tokkyo Koho Sho 59-213,728 (1984); hydroxyl-terminated polyorganosilsesquioxanes are allowed to react with a hexaorganodisilazane [EURO. PAT. No. 0516144A1 and Japan Kokai Tokkyo Koho Hei 4-353,521 (1992). It is also known that methylsilsesquioxanes containing terminal hydroxyl or alkoxy groups are trimethylsilylated by treating with hexamethyldisiloxane in the presence of an acid catalyst [Japan Kokai Tokkyo Koho Hei 7-70,321 (1995).
As mentioned above, a variety of procedures are known for linking reactive functional groups of a different kind to the side chain or end of a molecular structure. Nearly all of them, however, are based on initial synthesis of ladder polyorganosilsesquioxanes containing hydroxyl groups (silanol groups) in the side chain or at the end followed by reaction with compounds containing functional groups reactive with the hydroxyl groups such as chlorosilanes, alkoxysilanes, isocyanatosilanes, and disilazanes. However, the polyorganosilsesquioxanes thus synthesized contain a small amount of silanol groups which have not contributed to polymerization or the aforementioned reaction and remain as defect or branched structure and this causes such problems as lowering of mechanical properties, heat resistance and loss of storage stability.
Now, a procedure based on the initial formation of cage or ladder polyorganosilsesquioxanes end-capped with a cage structure and the subsequent direct introduction of functional groups solely at the end would conceivably give polymers that hardly contain silanol groups inside as branched structure and that show excellent storage stability and properties of good reproducibility such as heat resistance. This procedure, however, is subject to the following restrictions in the course of synthesis.
The synthesis of cage or ladder polyorganosilsesquioxanes based on hydrolysis of an organotrichlorosilane followed by polymerization in the presence of an alkaline rearrangement and condensation catalyst as described in the aforementioned Japan Tokkyo Koho Sho 40-15,989 (1965) and Japan Kokai Tokkyo Koho Sho 50-139,900 (1975) gives polymers that terminate in a cage structure and are virtually devoid of hydroxyl groups as disclosed in Japan Kokai Tokkyo Koho Sho 57-18,729 (1982) and Japan Kokai Tokkyo Koho Sho 59-213,728 (1984); hence, the aforementioned procedure for introducing reactive functional groups solely to the end cannot be adopted here. In consequence, the preparation of hydroxyl-terminated polyorganosilsesquioxanes has been greatly restricted as it requires either the use of special chloroformate esters and carbodiimides as catalysts or the adoption of any one of the procedures disclosed in Japan Kokai Tokkyo Koho Sho 50-11,197 (1975), Japan Kokai Tokkyo Koho Sho 50-11,198 (1975), Japan Kokai Tokkyo Koho Sho 50-11,199 (1975), and Japan Kokai Tokkyo Koho Sho 53-88,099 (1978).
Under these circumstances, it is an object of this invention to provide polyorganosilsesquioxanes of excellent storage stability and properties of good reproducibility such as heat resistance which are free of silanol groups as defect and branched structure inside and possess reactive functional groups at the ends and to provide a simple and commercially viable process for preparing polyorganosilsesquioxanes without having recourse to hydroxyl-terminated polyorganosilsesquioxanes.
The present inventors have conducted studies to accomplish the aforementioned objective, found that an equilibrium reaction between cage-terminated and hydroxyl-free polyorganosilsesquioxanes and functional group-containing disiloxanes in the presence of an alkaline catalyst readily yields polyorganosilsesquioxanes containing terminal reactive functional group X, and completed this invention.